Joining of multi-section ceramic molds

ABSTRACT

The several mating preformed parts of a multi-part ceramic mold are held in assembled relation by a surrounding ring that closely engages the mold. The ring may be slid over the mold or may be formed in place on the mold to be in intimate contact therewith and become a permanent part of the mold. The ring may have an integral pouring cup if the ring is to be at the top of the mold.

United States Patent [191 Hayes et al.

[ Dec. 23, 1975 1 JOINING OF MULTl-SECTION CERAMIC MOLDS [75] Inventors: Douglas R. Hayes, Vernon, Conn.;

Charles M. Phipps, Ridgewood, NJ.

[73] Assignee: United Technologies Corporation, Hartford, Conn.

[22] Filed: Aug. 21, 1974 [21] Appl. No.: 499,224

[52] US. Cl. 164/25; 164/60; 164/137;-

[51] Int. Cl. ..B22C 9/24; B22D 25/06;.

B22D 33/04 [58] Field of Search 164/23, 24, 25, 26, 60, 164/137, 341,349, 361, 364, 365; 249/164 [56] References Cited UNITED STATES PATENTS 12/1917 Meister 249/164 X l 1/1939 Lindsay 249/154 X 3,515,205 6/1970 Wickstrand 164/60 X 3,627,015 12/1971 Giamei et al. 164/60 3,690,368 9/1972 Copley et al 164/361 X 3,802,482 4/1974 Phipps 164/71 FOREIGN PATENTS OR APPLICATIONS 10,225 12/1898 United Kingdom 164/137 Primary Examiner-Francis S. Husar Assistant Examiner-John E. Roethel Attorney, Agent, or Firm-Charles A. Warren [57] ABSTRACT The several mating preformed parts of a multi-part ceramic mold are held in assembled relation by a surrounding ring that closely engages the mold. The ring may be slid over the mold or may, be formed in place on the mold to be in intimate contact therewith and become a permanent part of the mold. The ring may have an integral pouring cup if the ring is to be at the top of the mold. a

22 Claims, 10 Drawing Figures U.S. Patent Dec.23,1975 sheetlofz 3,927,710

JOINING OF MULTI-SECTION CERAMIC MOLDS BACKGROUNDOFTHEINVENTION Field of the Invention This invention relates to the casting of columnar grained or equiaxed articles particularly from high temperature alloys in a multi-part'mold made up of a plurality of mold elements. Such articles may be conventionally cast or columnar grained or may be cast from some of the eutectics.

SUMMARY OF THE INVENTION The preformed or precast parts of a multi-part mold as described in applicants copending application Ser. No. 416,563, filed Nov. 16, 1973 must be held together securely in assembled relation when the mold is poured to assure no leakage from the mold and to assure'the desired precision in the finished casting. The securing means must be able to withstand the heat to which the mold is heated which, in columnar grain casting, for example, is a temperature above the melting point of the alloy. Thus metallic clamps are not readily usable. The clamp must have thermal characteristics similar to those of the mold, such as the coefficient of thermal expansion, to avoid localized stressing of either the mold or the clamp.

According to the invention, a high strength ceramic ring is positioned around the multi-part mold at one or more locations along its length, the ring being a close fit to the outer surfaces of the mold in order to hold the mold parts in proper assembled relation. The ring may be a close slidable fit or it may be formed on the assembled mold parts to be essentially an integral part of the mold. The ring may be separatelyformed to be positioned around the mold or cast around the assembled mold or formed by the shell molding process in dipping a part of the mold in a ceramic slurry and drying the coating of ceramic formed thereon, the dipping and drying process being repeated until a coating of the desired strength is obtained. According to one feature the ring may'have an integral pouring cup if the ring is positioned atthe top of the mold. As an alternative to the ring, high strength ceramic clip or holding means may be positioned over the mating flanges of the mold parts.

The foregoing and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of preferred embodiments thereof as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevation of a mold with the invention in position.

FIG. 2 is a sectional view along line 22 of FIG. 1.

FIG. 3 is an elevation of a mold' as in FIG. 1 with a modified form of holding ring.

FIG. 4 is a sectional view along line 44 of FIG. 3.

FIG. 5 is an elevation of a mold with other forms of rings thereon.

FIG. 6 is a sectional view along line 66 of FIG. 5.

FIG. 7 is a fragmentation elevationof the top of the mold with a modified formofthe ring of FIG. 1, with parts broken away to showtheconstruction.

FIG. 8 is a view similar to FIG. 7 of a modification of theringofFIG.5.

a holding ring of FIG. 9 is a further modification shown in elevation. FIG. 10 is a sectional view along line 10-10 of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 1 and 2 the preformed multipart mold is shown by way of example for making the opposed halves of a turbine blade as described and claimed in the copending application Ser. No. 416,563 above identified. The mold includes preformed opposed mold sides 10 and 12 of a suitable ceramic and a center divider 14 also of a ceramic. The divider has edge flanges 16 and 18 received in notches in cooperating edge flanges 20 and 22 on one edge of sides 10 and 12 and other cooperating edge flanges 24 and 26 on the opposite edges of sides 10 and 12.

The mold sides 10 and 12 may have hold down flanges 28 at one end by which the mold, when assembled is held in position on a chill plate. Although the mold has other uses, such a mold construction is particularly useful in casting columnar grained articles of the type claimed in VerSnyder US Pat. No. 3,260,505 or Piearcey US. Pat. No. 3,494,707. The latter single crystal cast article is a particular form of columnar grain. This type of mold is also usable in casting eutectics such as described in Gell US. Pat. No. 3,567,526, which are also columnar grained.

Such molds must be held in secure assembled arrangement during the casting operation and the holding device must be such as not to be destroyed by the step of heating the mold to a temperature above the melting point of the alloy and also such as not to be overstressed or to overstress the mold parts during the heating operation or during the subsequent relatively fast cooling. 0

To accomplish this, the mold parts are surrounded at the desired'location lengthwise of the mold parts by a ceramic ring 32 cast of high strength ceramic material. This ring has an inner surface 34 the contour of which closely fits the outer surfaces of 'thefinold parts, at least at the mating flanges 20 and 2.2 at one edge and the opposite mating flanges 24 and 26.]Thereis just enough clearance to permit the ring toslide down over the assembled mold to the desired portion on the mold. Although the inner surface of the 'ring is shown as closely fitting over the entire area of the mold adjacent thereto, it is obvious that the particular'close fit is at the mating flanges. For this type of ring to be usable the mold must be the same size or smaller from the ring area to the top of the mold so that the ring may slide into position; Once the ring is in place it may be additionally secured by a suitable cement, not shown.

In the arrangement shown the mold has an enlargement 35 near the base to form the root portion of the blade, above which is the airfoil portion 36 of the mold and the ring 32 is shaped tofit the mold at the'enlargement 34 as shown. The cast articles are formed in the mold cavities 37 and 38. i

' As an alternate to the ring of FIGS. 1 and 2, the holding ring may be molded around the mold as in FIGS. 3 and 4. In this arrangement the mold parts 42 and 44 have the mating edge flanges 46 and 48 and the enlarged root portion 50 below the airfoil portion 52. This mold construction also has a shroud area 54 at the top of the airfoil portion such that the sliding ring of FIGS. '1 and 2 cannot be used. Instead, the ring 56 is formed in a ring mold, not shown, positioned around the mold. Moldable high strength ceramic is packed in the ring mold to form the ring 56 and, after suitable hardening by heating mold and ring, the ring mold is removed to produce the structure shown. Here the inner surface 57 of the ring is in intimate and permanent engagement with the mold parts 42 and 44. Thus these mold parts are held in secure engagement with each other during the casting operation. The material of ring 56 may obviously be any of the known high strength moldable ceramics and not necessarily the same material as the ceramic mold parts 42 and 44. By using different materials, the differential thermal expansion may be used to enhance the clamping action. The ring may be located at any position desired lengthwise of the mold. More than one of these rings may frequently be helpful in holding the mold parts securely togpher, such as the second ring 58 at the top of the mo Another form of holding ring for the multi-part mold is shown in FIGS. and 6. Here the mold sides 62 and 64 with mating edge flanges 66 and 68 and a central mold divider 70 are held together at top and bottom by rings 72 and 74, the latter enclosing the bottom flanges 76.

Each of these rings is formed by suitably holding the mold parts together between the ends as by a stretchable band, not shown, around the non-coated portion. Each end is then dipped in a ceramic slurry to form a coating, and then dried, with the dipping and drying being repeated enough times to produce the desired thickness of coatingto form a ring of adequate strength around the mold. After each dipping the wet dip coat may be coated with a granular ceramic. This is the procedure used to form a shell mold and after the desired ring thickness is obtained, the mold with the rings thereon is baked as in an oven to cure the material of the rings. In this way a suitable holding ring is produced with adequate strength to hold the mold parts in place for a casting operation.

To prevent the inner mold cavities from being contaminated by the slurry in making the rings 72 and 74 the ends of theimold assembly may be temporarily closed as by a sheet of cardboard or the like adhered thereto. Eitherring 72 or 74 may be formed independently of the other and only one ring may be used in certain mold structures. In any event the holding rings are securely attached to and form a permanent connection with the molds. The ring material is removed from the cast articles in the same manner as the mold material.

Theslidable ring of FIGS. 1 and 2 may be modified, if placed on the top end of the mold as in FIG. 7. Thus the ring 80, slidably mounted on the top end of the multi-part mold 82, has an integral filler cup 84 cast with the ring. The cup forms a shoulder 85 that limits the position of the ring on the mold. The cup' receives the molten alloy when the mold is being poured and directs it into the mold. THe ring thus serves both to hold the mold parts in assembled relation and as a filler cup. The ring and filler cup are molded into the configuration shown and baked to harden the ceramic before positioning them on the mold assembly.

Instead of a ring and integral filler cup positionable on the mold, the ring may be formed on the mold by the shell molding process. Thus as in FIG. 8, a shell mold type of coating 86 is formed on the upper end of the mold 88, but in this arrangement a wax pattern 89 positioned on the top of the mold forms a filler cup 90 that is integral with the ring 92. Both elements and 92 are simultaneously formed by dipping and drying the end of the mold as above described with reference to FIGS. 5 and 6 until the desired thickness of ring is produced. The ring produced in this way becomes securely and permanently a part of the mold and performs its holding function while the mold is poured.

In some circumstances the presence of a surrounding ring as described may affect the cooling of the alloy after the mold is poured. To avoid this the mold halves 92 and 94, FIGS. 9 and 10, may be held together by a shell mold type of coating located only along the mating side flanges 96 and 98. To do this, these side flanges are repeatedly dipped in a slurry for coating and then dried to build up a holding clip 100 and 102 that over lies the edge flanges but does not cover the parts of the mold directly external to the part being cast. Again the material used is a high strength ceramic which is hardened as by baking after the desired thickness is obtained thereby to obtain the desired strength. These clips are essentially a permanent part of the assembled mold when the latter is ready to be used and serve to hold the opposed mold halves securely in desired relation during the casting operation.

Although the drawings show a three-part mold including a center element, it is obvious that the invention is equally applicable to a two-part mold.

Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be understood by those skilled in the art that various changes and omissions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention.

Having thus described typical embodiments of our invention, that which we claim as new and desire to secure by Letters Patent of the United States is:

l. A holding device for use with a multi-part mold for the casting of high temperature metallic alloys, the mold including:

opposed precast ceramic mold sides having pro ecting mating edge flanges and having recesses therein to form an article cavity, the holding device being a high strength ceramic ring tightly surrounding the opposed mold sides and engaging the edge flanges to hold the opposed sides together, said rmg extending a part only of the length of the mold sides and said ring having a compatible thermal expansion to that of the mold sides. I

2. A holding device as in claim m which the ceramic ring is integrally connected with the mold sides.

3. A holding device as in claim 1 in which the rmg includes a pouring cup. I

4. A holding device as in claim 1 in wh ch the rmg IS hardened after positioning on the mold sides.

5. In the attachment of preformed ceramic mold parts together, said mold parts having mating edge n es, the ste s of: diiping at legst a part of the assembled mold elements including a part of the edge flanges in a ceramic slurry of the shell mold type to form a coating in the form of a ring thereon;

drying the coating; and I repeating the dipping and drying until a holding ring of the desired thickness is obtained. I

6. The process of claim 5 including the step of dipping both ends of the assembled mold elements to form a holding ring at each end.

7. The process of claim including a first step of forming a pouring cup pattern on the end of the assembled mold parts, and then dipping and drying the pattern and the portion of the mold adjacent thereto to form a shell pouring cup integral with a holding ring at the top of the mold parts.

8. The process of claim 5 in which the portions of the assembled mold elements to be coated are at least the outer side surfaces of the mating edge flanges.

9. The process of claim 5, in which the assembled mold elements have clamping flanges at an end and are open at that'end to rest on a chill'plate, and in which the flanges and adjacent portions of the assembled mold elements are the areas of the mold elements to be treated by the process.

10. The combination with a multi-part preformed ceramic mold having internal mating surfaces between which an article is cast, of means for holding the parts in assembled relation including a ring of high strength ceramic material surrounding a part of the mold, said ring having an inner surface conforming substantially to the cross-sectional shape of the mold within the ring and being of a material having a thermal expansion compatible with the mold material.

11. The combination as in claim in which the ring is integrally bonded to the mold where the ring surrounds it.

12. The combination as in claim 10 in which the ring is located at the top of the assembled multi-part mold and has an integral filler cup.

13. The combination as in claim 12 in which the ring is slidable over the top of the mold.

14. The combination as in claim 10 in which the mold is formed to be at least as small as the opening in the ring from the location where the ring is positioned to one endof the multi-part mold for placing the ring in position.

15. The combination as in claim 10 in which the ring 16. A multi-part mold including at least opposed ceramic side plates with projecting edge flanges having cooperating surfaces to hold the side plates in assembled casting position, and means surrounding the side plates for a portion of the length of the mold to hold the plates together, said means being a high strength ceramic ring extending completely around the assembled mold and having an inner surface conforming to substantially the outer surfaces of the projecting edge flanges of the side plates of the mold engaged thereby to hold the opposed side plates in casting position.

17. A multi-part mold as in claim 16 in which the ring is in bonded relation to the underlying surfaces of the mold.

18. A multi-part mold as in claim 16 in which the ring is slidable on the mold surfaces from one of the mold to its operative position thereon.

19. A multi-part mold as in claim 16 inwhich the ring engages the top portions of the mold parts and has an integral filler cup.

20. The method of securing the several preformed ceramic parts of a multi-part mold including opposed side plates having projecting cooperating flanges on opposite edges by:

holding the parts in assembled relation; forming a ring of ceramic material around a part of the mold to include the opposed projecting flanges and in permanent engagement therewith; and

heating the mold and ring to harden the material of the ring;

21. The method as in claim 20 in which the step of forming the ring is accomplished by placing a form around the mold and filling the form with ceramic material in intimate contact with the mold parts.

22. The method as in claim 20 in which the step of forming the ring is accomplished by successively dipping a part of the mold in a ceramic slurry to form a coating and drying the coating, and repeating the dipping and drying to product a ring of the desired thickis formed by dipping the mold in part in a ceramic ness.

slurry and drying and hardening the dip coat.

UNZ'EEHB seams PATENT same]; CERTEFICATE ()F CORRECTION PATENT NO. 3,927,710 DATED December 23, 1975 INVENTOR(S) Douglas R. Hayes et a1 It is certrfied that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 18, column 6 line 16:

"product" should read ---produce--o Signed and Sealed thisthirtieth D f March 1976 Claim 22, column 6 line 39:

[SEAL] A ttes r.-

C. MARSHALL DANN Commissioner oj'Parenrs and Trademarks RUTH C. MASON Arresting ()ffr'rer UNI'EEI) S'IATES PATENT UFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,927,710 DATE 1 December 23, 1975 INVENTOR(S) Douglas R. Hayes et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 18, column 6 line 16: after the Word "one" insert --end--.

Claim 22, column 6 line 39: "product" should read --produce-- Signed and Scaled thisthirtieth D ay of March 1 9 76 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mmnissiuner oj'Patenls and Trademarks 

1. A holding device for use with a multi-part mold for the casting of high temperature metallic alloys, the mold including: opposed precast ceramic mold sides having projecting mating edge flanges and having recesses therein to form an article cavity, the holding device being a high strength ceramic ring tightly surrounding the opposed mold sides and engaging the edge flanges to hold the opposed sides together, said ring extending a part only of the length of the mold sides and said ring having a compatible thermal expansion to that of the mold sides.
 2. A holding device as in claim 1 in which the ceramic ring is integrally connected with the mold sides.
 3. A holding device as in claim 1 in which the ring includes a pouring cup.
 4. A holding device as in claim 1 in which the ring is hardened after positioning on the mold sides.
 5. In the attachment of preformed ceramic mold parts together, said mold parts having mating edge flanges, the steps of: dipping at least a part of the assembled mold elements including a part of the edge flanges in a ceramic slurry of the shell mold type to form a coating in the form of a ring thereon; drying the coating; and repeating the dipping and drying until a holding ring of the desired thickness is obtained.
 6. The process of claim 5 including the step of dipping both ends of the assembled mold elements to form a holding ring at each end.
 7. The process of claim 5 including a first step of forming a pouring cup pattern on the end of the assembled mold parts, and then dipping and drying the pattern and the portion of the mold adjacent thereto to form a shell pouring cup integral with a holding ring at the top of the mold parts.
 8. The process of claim 5 in which the portions of the assembled mold elements to be coated are at least the outer side surfaces of the mating edge flanges.
 9. The process of claim 5 in which the assembled mold elements have clamping flanges at an end and are open at that end to rest on a chill plate, and in which the flanges and adjacent portions of the assembled mold elements are the areas of the mold elements to be treated by the process.
 10. The combination with a multi-part preformed ceramic mold having internal mating surfaces between which an article is cast, of means for holding the parts in assembled relation including a ring of high strength ceramic material surrounding a part of the mold, said ring having an inner surface conforming substantially to the cross-sectional shape of the mold within the ring and being of a material having a thermal expansion compatible with the mold material.
 11. The combination as in claim 10 in which the ring is integrally bonded to the mold where the ring surrounds it.
 12. The combination as in claim 10 in which the ring is located at the top of the assembled multi-part mold and has an integral filler cup.
 13. The combinaTion as in claim 12 in which the ring is slidable over the top of the mold.
 14. The combination as in claim 10 in which the mold is formed to be at least as small as the opening in the ring from the location where the ring is positioned to one end of the multi-part mold for placing the ring in position.
 15. The combination as in claim 10 in which the ring is formed by dipping the mold in part in a ceramic slurry and drying and hardening the dip coat.
 16. A multi-part mold including at least opposed ceramic side plates with projecting edge flanges having cooperating surfaces to hold the side plates in assembled casting position, and means surrounding the side plates for a portion of the length of the mold to hold the plates together, said means being a high strength ceramic ring extending completely around the assembled mold and having an inner surface conforming to substantially the outer surfaces of the projecting edge flanges of the side plates of the mold engaged thereby to hold the opposed side plates in casting position.
 17. A multi-part mold as in claim 16 in which the ring is in bonded relation to the underlying surfaces of the mold.
 18. A multi-part mold as in claim 16 in which the ring is slidable on the mold surfaces from one of the mold to its operative position thereon.
 19. A multi-part mold as in claim 16 in which the ring engages the top portions of the mold parts and has an integral filler cup.
 20. The method of securing the several preformed ceramic parts of a multi-part mold including opposed side plates having projecting cooperating flanges on opposite edges by: holding the parts in assembled relation; forming a ring of ceramic material around a part of the mold to include the opposed projecting flanges and in permanent engagement therewith; and heating the mold and ring to harden the material of the ring.
 21. The method as in claim 20 in which the step of forming the ring is accomplished by placing a form around the mold and filling the form with ceramic material in intimate contact with the mold parts.
 22. The method as in claim 20 in which the step of forming the ring is accomplished by successively dipping a part of the mold in a ceramic slurry to form a coating and drying the coating, and repeating the dipping and drying to product a ring of the desired thickness. 